Projection device

ABSTRACT

A projection device According to the present invention there is provided a projection device ( 30,50,100 ) comprising, a light source ( 31,61 ) which can provide light beams ( 32   a,b,c    62   a,b,c ), wherein the light beams ( 32   a,b,c    62   a,b,c ) can be used to define one or more pixels of a virtual image ( 48 ); a MEMS micro mirror ( 34 ) which is arranged to receive the light beams ( 32   a,b,c    62   a,b,c ) provided by the light source ( 31,61 ), and wherein the MEMS micro mirror ( 34 ) can oscillate about at least one oscillation axis ( 7,17 ) to scan the light beams ( 32   a,b,c    62   a,b,c ); a reflective element ( 38 ), which comprises a plurality of convex reflective projections ( 39 ), and wherein the reflective element ( 38 ) is arranged so that light beams ( 32   a,b,c    62   a,b,c ) reflected by the MEMS micro mirror ( 34 ) are incident on said convex reflective projections ( 39 ), so that the light beams ( 32   a,b,c    62   a,b,c ) are reflected by the convex reflective projections ( 39 ); a beam combiner ( 45,81 ), wherein the beam combiner is arranged to receive the light beams ( 32   a,b,c    62   a,b,c ) which are reflected by the convex reflective projections ( 39 ) wherein the beam combiner ( 45,81 ) is configured to at least partially reflect the light beams ( 32   a,b,c    62   a,b,c ) which it receives so that the light beams ( 32   a,b,c    62   a,b,c ) can form a virtual image ( 48 ) which is visible when viewed from within an eyebox ( 47 ). There is further provided a corresponding method of projecting a virtual image.

FIELD OF THE INVENTION

The present invention relates to a projection device and inparticularly, but not exclusively, to a projection device whichcomprises a diffuser in the form of a reflective element which comprisesa plurality of reflective convex projections which reflect light beamsto a beam combiner to project a virtual image. There is further provideda corresponding method of projecting a virtual image.

DESCRIPTION OF RELATED ART

Most projection devices use a diffuser to reduce the occurrence of thespeckle in the projected image

In most cases a micro-lens array is used as a diffuser. Typically themicro-lenses in a micro-lens array are convex lenses and are sizedbetween 10 to 500 μm. The micro-lens arrays are transparent duringoperation; thus the light beams must be transmitted through themicro-lenses in the micro-lens array in order to be diffused.Disadvantageously when the light beams are transmitted through themicro-lenses in the micro-lens array the light beams are diffracted andlarge amounts of light loss will occur in the micro-lens array.Furthermore, a large amount of parasitic light is created when the lightbeams are transmitted through the micro-lenses in the micro-lens array;this parasitic light creates speckle and/or visual parasitic patterns inthe projected image as well as reducing the overall contrast betweenadjacent pixels.

In most micro-lens arrays the micro-lenses are held in their arrayformation by means of a transparent holder portion. Typically thetransparent holder portion is composed of glass. The light beams mustfirst transmit through the transparent holder portion before reachingthe micro-lenses. The transparent holder portion thus further increasesthe amount of diffraction and light loss and also increases the amountof parasitic light which is created. The transparent holder portion, aswell as the transparent lenses, can further generate chromaticaberration.

Accordingly a projection device which uses any of the above-mentionedmicro-lens arrays will be unable to project a high quality image due tothe large amounts of diffraction, light loss, parasitic light, andchromatic aberration.

Other micro-lens arrays comprise an array of reflective micro-lenseseach of which have a concave profile. Moulds to manufacture suchmicro-lens arrays in high volume are very difficult to manufacture asthe junctions between successive lens need to be pointed; if thejunctions between successive lens are not pointed enough the junctionwill produce a lot of parasitic reflection during use which willdecrease the quality of the projected image. Thus it is difficult, andexpensive, to produce high volume projection systems, which usemicro-lens arrays which comprise an array of micro-lenses each of whichhave a reflective concave profile, and which can project a good qualityimage.

Furthermore a micro-lens array, which comprises an array of reflectivemicro-lenses each of which have a concave profile, will focus the lightbeams it receives; the focused light beams pose a risk to users as thefocused light beams may possess enough light energy to damage a user'seyes or accidentally ignite dust particles (for example, dust particlesfound on car windshields or dust particles on the dashboard of a car, ifsuch projection devices are used in a car).

Additionally a projection device which uses any of the above-mentionedmicro-lens arrays will not be compact, since in the case of micro-lensarrays which comprise convex lenses the microlens array must be placedbetween the projector and the combiner screen (e.g. in a head-up-displayprojection system), and in the case of micro-lens arrays which comprisereflective micro-lenses which have a concave profile, the light that isreflected on the reflective concave micro-lens array is first focused atthe focal distance of those lenses before it starts to diffuse towardsthe combiner screen, therefore the distance between the diffuser and thecombiner is larger to achieve the same image size in the combiner.

BRIEF SUMMARY OF THE INVENTION

According to the invention, there is provided a projection devicecomprising, a light source which can provide light beams, wherein thelight beams can be used to define one or more pixels of a virtual image;a MEMS micro mirror which is arranged to receive the light beamsprovided by the light source, and wherein the MEMS micro mirror canoscillate about at least one oscillation axis to scan the light beams; areflective element, which comprises a plurality of convex reflectiveprojections, and wherein the reflective element is arranged so thatlight beams reflected by the MEMS micro mirror are incident on saidconvex reflective projections, so that the light beams are reflected bythe convex reflective projections; a beam combiner, wherein the beamcombiner is arranged to receive the light beams which are reflected bythe convex reflective projections, wherein the beam combiner isconfigured to at reflect at least some of the light beams which itreceives so that the light beams can form a virtual image which isvisible when viewed from within an eyebox.

Since the beam combiner is configured to at reflect at least some of thelight beams which it receives, at least part of the light which the beamcombiner receives will be reflected by the beam combiner; the part ofthe light which is reflected will be used to form a virtual image.

In one embodiment the beam combiner may be semi-reflective andsemi-transparent. As the beam combiner is semi-reflective the beamcombiner will at reflect at least some of the light beams which itreceives; since the beam combiner and semi-transparent it will alsoallows a viewer to see through the beam combiner. The light beams whichare reflected form a virtual image which is visible when viewed fromwithin an eyebox.

The virtual image is formed behind the beam combiner. The virtual imageis created by the light beams which are reflected by the combiner. Thelight beams reflected by the convex reflective projections are divergingand are reflected by the combiner. A virtual image is formed, at theposition where extrapolations of the divergent light beams intersect.The extrapolations of the divergent light beams intersect at a positionbehind the beam combiner; accordingly the virtual image will appearbehind the beam combiner and not on the surface of the beam combiner,hence the term virtual image. The virtual image is formed only by thelight beams which are reflected by the beam combiner. The light beamswhich are not reflected by the beam combiner, are transmitted throughthe beam combiner and are lost; the light beams which are transmittedthrough the beam combiner are not used to project the virtual image.

After the light beams have been reflected by the convex reflectiveprojections in the reflective element the light beams will be diffused.Each of the diffused light beams will form a light cone. At least partof the diffused light beams are reflected by the beam combiner. Theeyebox is defined by the volume in which the light cones of all thelight beams which are reflected by the convex reflective projections onthe reflective element and subsequently reflected by the beam combiner,overlap.

The beam combiner can be thin film coated by dielectric or metal layersso that a part of light is transmitted through the coating and the otherpart is reflected. Fresnel's law equations determine the amount of lightwhich is reflected and transmitted by the dielectric coating. Formetallic coating the thickness of metal is preferably less than theevanescent penetration depth of the light beams to allow light to bepartially transmitted and partially reflected.

The reflective element acts as a diffuser to diffuse the light beams andreduce the occurrence of speckle in the virtual image.

As the light beams are reflected by the convex reflective projectionsthe light beams do not transmit through an optical component (such as amicro-lens array); accordingly there is no diffraction of the lightbeams and there is a reduction of the amount of light loss and parasiticlight. Therefore the projected image will show an enhanced contrast.

Additionally, since the convex reflective projections are used toreflect the light beams this obviates the need for a holder portion.Consequently there is no chromatic aberration generated.

Also, the mould needed to manufacture the convex reflective projectionsin volume is easier to make than the mould needed to manufacturemicro-lens arrays which comprise concave reflective micro-lenses, asthere is no requirement to provide pointed interfaces between thereflective projections. Accordingly, it is easier to manufacture theprojection device of the present invention.

Furthermore since the convex reflective projections in the reflectiveelement are convex, the reflected light beams will be diffused ratherthan focused. The light beams are never focused by the reflectiveelement. Accordingly, the danger posed to a user's eyes is reduced.

Finally, as the light beams are reflected by the convex reflectiveprojections of the reflective element, the focal point of the reflectiveelement is located behind the convex reflective projections. Accordinglythe length of the projection device can be reduced by an amount equal totwice the focal length of the reflective element to provide a morecompact projection device.

It should be understood that the reflective element used in theprojection device of the present invention may be manufactured using anyof; hot embossing, nano-imprinting; roll-to-roll, diamond turning,photolithography patterning followed by a step of reflow, injectionmoulding, or etching (dry and/or wet). The manufacturing process mayalso include depositing a reflective layer which defines the reflectiveelement, on a micro lens array which comprises array of convex lenses,where appropriate.

It will be understood that the light source may provide one or morelight beams which define one or more pixels of an image. For example,the light source may provide a red, green and blue light beam which maybe combined to define coloured pixels of the virtual image.

The reflective element may comprise a metallic sheet which comprises anarray of convex projections.

The reflective element may comprise a micro-lens array, which comprisesan array of reflective micro-lenses each of which have a convex profile.The reflective element may comprise a micro-lens array which comprisesan array of convex micro-lenses, and a reflective layer which is mountedon a surface of micro lens array to form convex reflective projections.The reflective layer is preferably mounted on a surface of the convexmicro-lenses to form convex reflective projections. The reflective layerpreferably is configured so that it does not transmit any light, inother words the reflective layer is fully reflective. The micro-lensarray may comprise a holder portion which holds the plurality of convexmicro-lenses. The holder portion may be transparent to light beams. Theconvex micro-lenses may also be transparent to light beams. However, aholder portion is not essential to the invention. In fact, because theprojection system of the present invention uses convex reflectiveprojections to reflect light, advantageously this obviates the need fora holder portion or a micro lens array. If the projection device isprovided with a holder portion then preferably the plurality of convexlenses are integral with the holder portion.

The reflective element is preferably arranged such that the convexreflective projections are closest to the MEMS micro mirror, than anyother part of the reflective element. The reflective element ispreferably arranged so that the convex reflective projections areclosest to the MEMS micro mirror, than any other part of the reflectiveelement, along a path followed by the light beams reflected from theMEMS micro mirror to the reflective element. This will ensure that theconvex reflective projections are first to receive the light reflectedby the MEMS micro mirror. In particular, this will ensure that the lightbeams are not transmitted through any part of the reflective element.Rather, the light beams will be reflected by the convex reflectiveprojections without having passed through any other part of thereflective element. For example, if the reflective element comprises amicro-lens array which comprises an array of convex micro-lenses, and areflective layer which is mounted on a surface of micro lens array toform convex reflective projections; then the reflective element willpreferably be arranged such that the reflective layer which is mountedon a surface of micro lens array is closest to the MEMS micro mirror andthe micro lens array is further away from the MEMS micro mirror. Thelight beams will thus be reflected by the convex reflective projectionswithout the light beams having been transmitted through the holderportion or the micro-lens array.

The reflective element may comprise at least one of; Al, Au, Chromium,Ag, Ti, a protective layer such as SiO₂, SiN, and/or dielectricmultilayer.

The convex reflective projections of the reflective element preferablyeach have a convex spherical profile.

The convex reflective projections of the reflective element may vary insize across the reflective element. The convex reflective projections ofthe reflective element may vary in their radius of curvature across thereflective element. The convex reflective projections of the reflectiveelement may be offset from being alignment to one another (for exampleperiodic, random or pseudo-random). The benefits of using, random orpseudo-random alignment reduces moiré effect because each reflectiveelement creates a diffraction pattern that averages-out. Convexreflective projections on the borders of the array may have largerradius enabling lower divergence, therefore reducing light loss becauseof the light that would transmit out of the beam combiner, whereas theconvex reflective projections around the centre may have smaller radiusof curvature so as that the reflected light has direction to cover thecombiner entirely.

The beam combiner may form a head-up-display.

After the light beams have been reflected by the convex reflectiveprojections in the reflective element the light beams will be diffused.Each of the diffused light beams will form a light cone. At least someof the diffused light beams are reflected by the beam combiner. Theeyebox is defined by the volume in which the light cones of all thelight beams which are reflected by the convex reflective projections onthe reflective element and subsequently reflected by the beam combiner,overlap. The size of the eyebox depends on the range of angles overwhich the beam combiner can receive light from the reflective element.This range of angles may depend on the size of the combiner, on thedistance between the diffuser and combiner and on the distance betweenthe virtual image and combiner. For example, a large combiner canreceive light from the reflective element over a large range of angles,accordingly the volume in which all light cones overlap will be largeand the thus the eyebox will be large; while a smaller combiner canreceive light from the reflective element over a smaller range ofangles, accordingly the volume in which all light cones overlap will besmall and the thus the eyebox will be small.

The virtual image is formed behind the beam combiner. The light beamsreflected by the convex reflective projections are diverging and areindecent on the beam combiner. Some of the light beams are reflected bythe beam combiner and remain divergent after the reflection and some ofthe beams are transmitted through the beam combiner. A virtual image isformed at the position where extrapolations of the divergent light beamswhich are reflected by the beam combiner intersect (the intersectionwill occur at a position which is behind the beam combiner).

As mentioned in one embodiment the beam combiner may be semi-reflectiveand semi-transparent. The light beams which are transmitted through thebeam combiner are lost; only those light beams which are reflected bythe beam combiner are used to form the virtual image.

In another embodiment the beam combiner may be fully reflective. In sucha case the projection device will further comprise a semi-reflectivesemi-transparent surface which receives light beams which are reflectedfrom the fully reflective beam combiner. The surface may be provided ona windshield. Since the surface is semi-reflective it will reflect atleast some of the light beams which it receives; since is surface isalso semi-transparent it will also allow a viewer to see through thesurface. The light beams which are reflected form a virtual image whichis visible when viewed from within an eyebox. The semi-reflectivesurface which is provided on a windshield may form a head-up-display.

After the light beams have been reflected by the convex reflectiveprojections in the reflective element the light beams will be diffused.Each of the diffused light beams will form a light cone. At least somethe diffused light beams are reflected by the beam combiner. The eyeboxis defined by the volume in which the light cones of all the light beamswhich are reflected by the convex reflective projections on thereflective element and subsequently reflected by the beam combiner,overlap. The size of the eyebox depends on the range of angles overwhich the semi-reflective semi-transparent surface which is provided ona windshield can receive light from the fully reflective beam combiner.This range of angles may depend on the size of the semi-reflectivesemi-transparent surface, on the distance between the beam combiner andsemi-reflective semi-transparent surface and on the distance between thevirtual image and semi-reflective semi-transparent surface. For example,a large semi-reflective semi-transparent surface can receive light fromthe fully reflective beam combiner over a large range of angles,accordingly the volume in which all light cones overlap will be largeand the thus the eyebox will be large; while a smaller semi-reflectivesemi-transparent surface can receive light from the fully reflectivebeam combiner over a smaller range of angles, accordingly the volume inwhich all light cones overlap will be small and the thus the eyebox willbe small.

The semi-reflective semi-transparent surface which is provided onwindshield is used to reflect some of the light beams which it receivesfrom the fully reflective beam combiner; only those light beams whichare reflected from the semi-reflective semi-transparent surface are usedto form the virtual image. Light beams which are transmitted through thesemi-reflective semi-transparent surface are not used to form thevirtual image. The shape of the windshield can affect the shape of thevirtual image by shifting the angle at which light beams are reflectedand also shifting the position of the light beams; this can causedistortion of the virtual image. The fully reflective beam combiner mayalso be configured to reduce distortion in the virtual image; forexample the fully reflective beam combiner may have a spherical oraspherical concave surface so that geometrical deformation due to thewindshield shape are compensated for.

Some of the light beams received at the semi-reflective semi-transparentsurface are reflected and some of the light beams received at thesemi-reflective semi-transparent surface are transmitted. The lightbeams which are reflected remain divergent after they have beenreflected and another part of the light beams are transmitted throughthe semi reflective surface. To create the virtual image thesemi-reflective surface which is provided on the windshield reflectspart of the light beams without focusing those parts of the light beamsso that the light beams which are reflected remain diverging afterreflection. A virtual image is formed at the position whereextrapolations of the divergent light beams which are reflected by thesemi-reflective surface intersect (the intersection will occur at aposition which is behind the semi-reflective surface which is providedon the windshield). Those light beams which are transmitted through thesemi-reflective semi-transparent surface are lost and are not used toform the virtual image.

The beam combiner can be made fully reflective by either a metal coating(wherein the thickness of the metal coating is larger than theevanescent field penetration depth of the light beams) or by reflectivedielectric coating which has a bandgap in the wavelength range ofinterest.

The projection device may further comprise one or more lenses which arearranged between the light source and the MEMS micro mirror, wherein theone or more lenses are configured to focus the light beams. Preferably aplurality of lenses is provided, each lens is provided between a lightsource and reflectors.

The one or more lenses may comprise a converging lens which can focusthe light beam. The one or more lenses may have a biconvex orplano-convex shape with aspheric, spheric, polynomial or free formconvex surfaces.

Preferably the one or more lenses are each configured to focus the lightbeams such that the light beams have a spot size on the reflectiveelement which has an area which is less than, or equal to, the area of asingle convex reflective projection.

It will be understood that it would be sufficient that the one or morelenses are located in an optical path followed by the light beamspassing from the light source to the MEMS micro mirror.

The light beams may be collimated light beams and the projection devicemay further comprise a biconvex lens, plano-convex lens, achromaticlens, telecentric lens, f-theta lens, and/or cylindrical convex lens,which is arranged between the MEMS micro mirror and the reflectiveelement, to focus the collimated light beams.

The projection device may comprise one or more converging lenses whichis arranged to receive light beams which are output from the so as toconvert the light beams into collimated light beams. Preferably thedistance between the light source and each of the one or more converginglenses is equal to the focal length of the respective converging lens.The light beams which are output from the one or more converging lenseswill be collimated. If the light source provides a red, green and bluelight beams, either the light beams are first combined and thencollimated, or each of the beams are individually collimated and thencombine after they have been collimated.

Preferably the telecentric lens is configured to focus the collimatedlight beams such that the light beams have a spot size on the reflectiveelement which has an area which is less than, or equal to, the area of asingle convex reflective projection. Preferably the distance between thetelecentric lens and the reflective element is equal to the focal lengthof the telecentric lens.

Preferably the area of the spot size will be 100 μm. Preferably the areaof the spot size will be less than 300 μm.

It will be understood that it would be sufficient that the telecentriclens is located in an optical path followed by the light beams passingfrom the MEMS micro mirror to the reflective element.

The telecentric lens maybe further configured to make the light beamsparallel. In other words the telecentric lens maybe further configuredto make the chief rays (or central ray) of each of the light beams to beparallel to each other, while each of the light beams may itself befocused onto the reflective element.

The light beams may be focused such that they have a spot size on thereflective element, which has an area which is less than, or equal to,the area of a single convex reflective projection.

The convex reflective projections of the reflective element may bearranged to lie on a curved plane.

Preferably the curved plane is a convex or a concave plane.

Preferably the curvature of the curved plane is equal to the curvatureof a curve along which the point at which the light beams which arereflected from the MEMS micro mirror focus (i.e. the focus point of thelight beams which are reflected from the MEMS micro mirror) moves, asthe MEMS micro mirror oscillates about its single oscillation axis. Thefocus point of light reflected by the MEMS micro mirror is the focalpoint of the lens which is arranged between the light source and theMEMS micro mirror to focus the light beams; or, in the embodiment whichcomprises a telecentric lens which focuses light beams, the focus pointof light reflected by the MEMS micro mirror is the focal point of thetelecentric lens.

As the MEMS micro mirror oscillates about a single oscillation axis, thefocus point of the light reflected by the MEMS micro mirror will bemoved over a curve (i.e. an arc). To ensure that the light beams arealways focused at the surface of the convex reflective projections inthe reflective element, as the MEMS micro mirror oscillated about itsoscillation axis, the convex reflective projections are arranged to lieon a curved plane whose curvature is equal to the curvature of the curveover which the focus point of the light reflected by the MEMS micromirror is moved when the MEMS micro mirror is oscillated about itssingle oscillation axis. In this manner the reflective element cancompensate for changes in the position of focus point of light reflectedby the MEMS micro mirror, which occurs when the MEMS micro mirroroscillates. Thus, the convex reflective projections of the reflectiveelement are located at the focus length of the light reflected by theMEMS micro mirror, even as the MEMS mirror oscillates about its singleoscillation axis.

Likewise the MEMS micro mirror may be oscillated about two orthogonaloscillation axes. In such a case it may be preferable to arrange theconvex reflective projections of the reflective element to lie on aspherical plane, or on an aspherical plane. The curvature of sphericalplane, or aspherical plane, is preferably such that it corresponds tothe curvature of a plane over which the focus point of the lightreflected by the MEMS micro mirror moves as the MEMS mirror oscillatesabout these two orthogonal oscillation axes. Thus in this manner thereflective element can compensate for changes in the position of focuspoint of light reflected by the MEMS micro mirror, which occurs when theMEMS micro mirror oscillates about its two orthogonal oscillation axes.Thus, the convex reflective projections of the reflective element arelocated at the focus length of the light reflected by the MEMS micromirror, even as the MEMS mirror oscillates about its two orthogonaloscillation axes.

The spherical plane preferably has a concave-spherical profile (i.e.bowl-shaped). The aspherical plane preferably has a concave-asphericalprofile.

The curved plane may be a concave-spherical or concave-aspherical plane.

The beam combiner may have a curved profile. The beam combiner has acurved profile to adapt the position and size of the virtual image to becomfortable for the viewer. The curved profile modifies the anglebetween the light beams which changes the position of where the virtualimage appears. Typically the more curved the beam combiner is, thefurther away from the beam combiner the virtual image will appear.

Preferably the beam combiner is arranged such that a concave surface ofthe beam combiner receives the light beams which are reflected by theconvex reflective projections of the reflective element.

A curved beam combiner will define a curved focal plane on which focalpoints of the beam combiner lay. As a result the virtual image willappear to be on a curved plane (i.e. on the curved focal plane), whichmay result in the virtual image appearing blurred.

Preferably the convex reflective projections of the reflective elementare arranged to lie on a curved plane, wherein the curved plane is aconvex plane. This will compensate for the effect of the curved beamcombiner. Specifically, this will ensure that the virtual image willappear to be on a planar plane, thus providing a clearer virtual image.

Preferably the curvature of the curved plane on which the convexreflective projections of the reflective element lie, is such that focalpoints of the beam combiner lie on a planar plane. In other words, thecurvature of the curved plane on which the convex reflective projectionsof the reflective element lie, is such that the focal points ofdifferent areas of the beam combiner will lie on the same planar plane.

Preferably the curvature of the curved plane on which the convexreflective projections of the reflective element lie, is equal to thecurvature of the beam combiner. Most preferably the curvature of thecurved plane on which the convex reflective projections of thereflective element lie, is equal to the curvature of the concave surfaceof the beam combiner on which light beams reflected by the reflectiveelement are incident.

The curved plane may be a convex-spherical or convex-aspherical plane.

The convex reflective projections of the reflective element may bearranged to lie on a on a spherical plane, or on an aspherical plane.The spherical plane preferably has a convex-spherical profile. Theaspherical plane preferably has a convex-aspherical profile.

The MEMS micro mirror may be arranged along the same axis as an axis onwhich the centre of the reflective element lies. In other words the MEMSmicro mirror may be arranged opposite to the centre of the reflectiveelement. The MEMS micro mirror may be aligned with the centre of thereflective element.

The reflective element is preferably oriented such that the light beamswhich are reflected from the MEMS micro-mirror to the reflective elementare incident on reflective element are non-perpendicular to a plane ofthe reflective element. The plane of the reflective element may be theplane on which the reflective element lies. The reflective element ispreferably oriented such that light beams, reflected by the MEMSmicro-mirror when the MEMS micro-mirror is in a non-actuated position(i.e. a rest position), are incident on the reflective element at anangle which is non-perpendicular to a plane of reflective element. Theplane of the reflective element may be the plane on which the reflectiveelement lies.

The MEMS micro-mirror may comprise a support frame and a micro mirrorattached to the support frame by means of two or more torsional arms.The two or more torsional arms define one or more oscillation axes forthe micro mirror.

The MEMS micro-mirror may be arranged such that a plane of the supportframe of the MEMS micro-mirror is off set from being parallel to the aplane of the reflective element lies. In other words the support frameof the MEMS micro-mirror and the reflective element will be arranged tobe non-parallel to one another. This will ensure that which themicro-mirror of the MEMS micro-mirror is in a neutral position, thelight beams reflected by the micro-mirror will be indecent on thereflective element at an angle which is greater than 0° and less than90°.

The projection device may further comprise an imaging system such asDLP/DMD (Digital Light Processing/Digital Micromirror array), LCOS(Liquid Crystal on Silicon) and/or LCD (Liquid Crystal Display). Thereflective element may be arranged so that the convex reflectiveprojections direct light to the imaging system. Because the light beamsare scanned by the oscillating MEMS mirror onto the reflective element,then as a result the light reflected by the convex reflectiveprojections is despeckled and therefore can serve as illuminating sourcewhich provides despeckled light to the second imaging device or to anyrandom surface.

The above-mentioned projection device could be used to form a head updisplay system. In such a system either the beam combiner or thesemi-reflective surface which is provided on a windshield, may form ahead-up-display.

A head-up display is any transparent or semi-transparent display thatpresents data without requiring users to look away from their usualviewpoints.

According to a further aspect of the present invention there is provideda method of projecting an image comprising the steps of; providing lightbeams which define one or more pixels of a virtual image, using a lightsource; reflecting the light beams using a MEMS micro mirror, andoscillating the MEMS micro mirror about at least one oscillation axis toscan the reflected light beams; receiving, at a reflective element, thelight beams which are reflected by the MEMS micro mirror, the reflectiveelement comprising a plurality of convex reflective projections, andwherein the reflective element is arranged so that light beams reflectedby the MEMS micro mirror are incident on said convex reflectiveprojections, so that the light beams are reflected by the convexreflective projections; reflecting the light beams using the convexreflective projections of the reflective element; receiving at a beamcombiner the light beams which have been reflected by the convexreflective projections of the reflective element; reflecting at leastsome of the light beams using the beam combiner so that the reflectedlight beams can form a virtual image which is visible from within aneyebox.

The method may comprise the step of using the projection device in ahead-up-display projection system. The method may comprise the step ofusing the beam combiner as a head-up-display.

The method may comprise the step or arranging the reflective elementsuch that the convex reflective projections of the reflective elementare closest to the MEMS micro mirror, than any other part of thereflective element. This will ensure that the convex reflectiveprojections of the reflective element are first to receive the lightbeams reflected by the MEMS micro mirror.

The method may further comprise the step of focusing the light beamsusing one or more lens which is located between the light source and theMEMS micro mirror.

The step of providing light beams may comprise providing collimatedlight beams and the method may further comprise the step of focusing thecollimated light beams using a lens. The lens may be biconvex lens,plano-convex lens, achromatic lens, telecentric lens, f-theta lens,and/or cylindrical convex lens, which is arranged between the MEMS micromirror and the reflective element.

The method may comprise the step of focusing the light beams so that thelight beams have a spot size on the reflective element, which has anarea which is less than, or equal to, the area of a single convexreflective projection.

The beam combiner may be semi-reflective and semi-transparent, and themethod may comprise the step of reflecting some of the light beams whichare incident on the beam combiner and and transmitting some of the lightbeams which are incident on the beam combiner, and using the reflectedlight beams to define a virtual image which is viewable from within aneyebox.

The beam combiner can be thin film coated by dielectric or metal layersso that some of the light beams are transmitted through the coating andsome of the light beams are reflected. Fresnel equations determine theamount of light beams which is reflected and transmitted by thedielectric coatings. For metallic coating the thickness of metal ispreferably less than the evanescent penetration depth of the lightbeams, to allow light to be partially transmitted and partiallyreflected.

The beam combiner may be fully reflective and the method may furthercomprise the reflecting some of the light beams and transmitting some ofthe light beams using a semi-reflective semi-transparent surface whichis provided on a windshield, to define a virtual image which is viewablefrom within an eyebox. The semi-reflective semi-transparent surfacewhich is provided on a windshield may be a head-up-display.

The beam combiner may be made fully reflective by providing a thickmetal coating (thicker than the evanescent field penetration depth) orby providing a reflective dielectric coating which has a bandgap in thewavelength range of interest.

The method may further comprise the step of arranging the MEMS micromirror so that it lies on the same axis as an axis on which the centreof the reflective element lies. In other words the method may comprisethe step of arranging the MEMS micro mirror so that it is opposite to acentre of the reflective element.

The method may comprise the step of arranging the reflective elementsuch that the light beams which are reflected from the MEMS micro-mirrorto the reflective element are incident on reflective element arenon-perpendicular to a plane of the reflective element. The plane of thereflective element may be the plane on which the reflective elementlies. The method may comprise the step of arranging the reflectiveelement such that light beams, reflected by the MEMS micro-mirror whenthe MEMS micro-mirror is in a non-actuated position (i.e. a restposition), are incident on the reflective element at an angle which isnon-perpendicular to a plane of reflective element. The plane of thereflective element may be the plane on which the reflective elementlies.

The MEMS micro-mirror may comprise a support frame and a micro mirrorattached to the support frame by means of two or more torsional arms.The two or more torsional arms define one or more oscillation axes forthe micro mirror. The method may comprise the step of arranging the MEMSmicro-mirror such that a plane of the support frame of the MEMSmicro-mirror is off set from being parallel to the a plane of thereflective element lies. In other words the method may comprise the stepof arranging the support frame of the MEMS micro-mirror and thereflective element to be non-parallel to one another. This will ensurethat which the micro-mirror of the MEMS micro-mirror is in a neutralposition, the light beams reflected by the micro-mirror will be indecenton the reflective element at an angle which is greater than 0° and lessthan 90°.

The MEMS micro-mirror may comprise a support frame and a micro mirrorattached to the support frame by means of two or more torsional arms.The two or more torsional arms define one or more oscillation axes forthe micro mirror. The method may comprise the step of arranging the MEMSmicro-mirror such that a plane of the support frame of the MEMSmicro-mirror is parallel to the reflective element but where the normalto the reflective element is not normal to the MEMS mirror supportframe. In other words the method may comprise the step of arranging thesupport frame of the MEMS micro-mirror and the reflective element to beparallel to one another but where the input light is not normal to thereflective element. Therefore in practice, the angle of the incidentlight beam on the reflective element, in regards to the normal of thereflective element, is greater than 0° and less than 90°. This angle canbe oriented in the vertical direction considering the HUDplanar/standard orientation. In that case, this will ensure that due tothis incident angle, the reflective element will not be viewed by thedriver as the combiner and the reflective element will not be on thesame height. This angle can be called indicatrix.

The method may further comprise the step of using the projection devicein a head up display system. The method may comprise the step of usingthe beam combiner as a head-up-display. The method may comprise the stepof using the semi-reflective surface which is provided on a windshieldas a head-up-display.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the aid of the descriptionof an embodiment given by way of example and illustrated by the figures,in which:

FIG. 1 provides an aerial view of a projection device according to anembodiment of the present invention;

FIG. 2 provides an aerial view of a projection device according to afurther embodiment of the present invention;

FIG. 3 provides an aerial view of a projection device according to afurther embodiment of the present invention;

FIGS. 4a and 4b show a MEMS micro mirror which is configured tooscillate about a single oscillation axis, and which may be used in anyof the projection devices shown in FIGS. 1-3;

FIG. 4c shows a MEMS micro mirror which is configured to oscillate abouttwo orthogonal oscillation axes, and which may be used in any of theprojection devices shown in FIGS. 1-3;

FIG. 5a shows how the focus point of the light reflected by the MEMSmicro mirror moves along a curved plane (an arc) as the MEMS micromirror oscillates about an oscillation axis;

FIG. 5b shows a preferred configuration for the reflective element usedin the projection devices shown in FIGS. 1-3, when the MEMS micro mirrorin the projection device is configured to oscillate about a singleoscillation axis;

FIG. 5c shows a preferred configuration for the reflective element usedin the projection devices shown in FIGS. 1-3, when the MEMS micro mirrorin the projection device is configured to oscillate about a twoorthogonal oscillation axis, or when the projection device comprises twoMEMS micro mirrors which can oscillate about a single oscillation axisand which are arranged in optical communication and such that theiroscillation axes are orthogonal;

FIG. 6a illustrates how a beam combiner which has a curved profile willfocus the virtual image onto a curved plane;

FIG. 6b shows an alternative configuration for the reflective elementused in the projection devices shown in FIGS. 1-3.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION

FIG. 1a is an aerial view of a projection device 30 according to anembodiment of the present invention.

The projection device 30 comprises a light source 31 which comprisesred, green and blue light sources 33 a,b,c which provide red, green andblue light beams 32 a,b,c respectively. The red, green and blue lightbeams 32 a,b,c, when combined, define one or more pixels of a virtualimage 48 which is projected by the projection device 30.

The projection device 30 further comprises a MEMS micro mirror 34 whichis arranged to receive the light beams 32 a,b,c provided by the lightsource 31. In this particular example the light source 31 comprisesreflectors 35 a,b,c which direct the red, green and blue light beams 32a,b,c, respectively, to the MEMS micro mirror 34.

The MEMS micro mirror 34 can oscillate about at least one oscillationaxis 7,17 to scan the light beams 32 a,b,c. As will be described in moredetail later the MEMS micro mirror 34 may be configured to oscillateabout a single oscillation axis 7 only, so that the MEMS micro mirror 34scans the light beams 32 a,b,c in one-dimension (i.e. along either thevertical or horizontal directions); or the MEMS micro mirror 34 may beconfigured to oscillate about two orthogonal oscillation axes 7,17, sothat the MEMS micro mirror 34 can scan the light beams 32 a,b,c intwo-dimensions (i.e. along both the vertical and horizontal directions).Alternatively, the projection device 30 may comprises two MEMS micromirrors 34 each of which has a single oscillation axis, and wherein thetwo MEMS micro mirrors 34 are arranged to be in optical communicationand such that their oscillation axes are orthogonal; two MEMS micromirrors 34 arranged in this manner can also achieve scanning of thelight beams 32 a,b,c in two-dimensions.

The projection device 30 has a reflective element 38, which comprises aplurality of convex reflective projections 39. The surface 40 of each ofthe convex reflective projections is fully reflective. The convexreflective projections 39 may comprise at least one of; Al, Au,Chromium, Ag, Ti, a protective layer such as SiO₂, SiN, and/ordielectric multilayer.

The reflective element 38 is arranged so that the light beams 32 a,b,creflected by the MEMS micro mirror 34 are incident on said convexreflective projections 39. The light beams 32 a,b,c are reflected by theconvex reflective projections 39.

In this particular example the reflective element 38 comprises ametallic layer which is mounted on the surface of a micro lens array 52which comprises a plurality of convex micro lenses 51. A holder portion43 holds the plurality of convex lenses 51 in their arrayedconfiguration. The plurality of convex lenses 51 are integral to theholder portion 43. The holder portion 43 and micro lens array 52 areboth transparent but the metallic layer which defines the reflectiveelement 38 is fully reflective. It should be understood that the holderportion 43 and micro lens array 52 are not essential to the invention;in fact, because the projection system 30 uses the reflective element 38only to reflect light beams 32 a,b,c, advantageously this obviates theneed for a holder portion 43 and micro lens array 52.

The reflective element 38 is arranged such that the convex reflectiveprojections 39 are closest to the MEMS micro mirror 34. In theprojection device 30 illustrated in FIG. 1 the reflective element 38 isarranged such that the convex reflective projections 39 are closest tothe MEMS micro mirror 34 and the holder portion 43 and micro lens array52 are further from the MEMS micro mirror 34; this will ensure that theconvex reflective projections 39 of the reflective element 38 are firstto receive the light beams 32 a,b,c reflected by the MEMS micro mirror34. In particular, this will ensure that the light beams 32 a,b,c arenot transmitted through any part of the holder 43 or micro lens array52; rather, the light beams 32 a,b,c will be reflected by the convexreflective projections 39 without the light beams 32 a,b,c having beentransmitted through any part of the holder 43 or micro lens array 52.

The projection device 30 further comprises lenses 41 a,b,c which arearranged between the respective red, green and blue laser sources 33a,b,c and reflectors 35 a,b,c of the light source 31. The lenses 41a,b,c are configured to focus the light beams 32 a,b,c. It will beunderstood that the lenses 41 a,b,c may be alternatively are arrangedbetween the reflectors 35 a,b,c and the MEMS micro mirror 34.

The lenses 41 a,b,c may each comprise a converging lens so that theyfocus the light beams 32 a,b,c. For example the lenses 41 a,b,c may eachcomprise a biconvex or plano convex shaped lens with aspheric, spheric,polynomial or free form convex surfaces.

In this example the lenses 41 a,b,c are configured to focus the lightbeams 32 a,b,c such that the light beams 32 a,b,c have a spot size onthe reflective element 38 which has an area which is less than, or equalto, the area of a single convex reflective projection 39 in thereflective element 38. Preferably, the area of the spot size will be 100μm or less.

It will be understood that it is not necessary for the lenses 41 a,b,cto be physically located between the reflectors 35 a,b,c and the MEMSmicro mirror 34; it would be sufficient that the lenses 41 a,b,c arelocated in an optical path followed by the light beams 32 a,b,c passingfrom reflectors 35 a,b,c to the MEMS micro mirror 34.

The projection device 30 further comprises a beam combiner 45. In thisparticular example the beam combiner 45 is semi-transparent andsemi-reflective. The beam combiner 45 is arranged to receive the lightbeams 32 a,b,c which are reflected by the convex reflective projections39 of the reflective element 38. The beam combiner 45 is shown to have acurved profile and is arranged such that a concave surface 46 of thebeam combiner 45 receives the light beams 32 a,b,c which are reflectedby the convex reflective projections 39 in the reflective element 38.

It will be understood that the light source may provide one or morelight beams which define one or more pixels of an image. For example,the light source may provide a red, green and blue light beam which maybe combined to define coloured pixels of the virtual image.

As the beam combiner 45 is semi-transparent and semi-reflective it willreflect some of the light beams which it receives and will transmit someof the light beams 32 a,b,c which it receives. The reflected light beams32 a,b,c only are used to project a virtual image 48. The transmittedparts of the light beams 32 a,b,c are lost and are not used to projectthe virtual image 48. The light beams which the beam combiner 45reflects are directed to a predefined area referred to as an eyebox 47.The eyebox 47 is an area within which the virtual image 48 is visible;outside the eyebox 47 the virtual image 48 is not visible. A user 49 canview the projected virtual image 48 only when they look at the virtualimage from a location within the eyebox 47.

The beam combiner 45 has a curved profile to adapt the position and sizeof the virtual image 48 to be comfortable for the viewer. The curvedprofile modifies the angle between the light beams 32 a,b,c adapt theposition and size of the virtual image 48.

The beam combiner 45 can be coated by dielectric or metal layers so thatsome of the light beams 32 a,b,c are transmitted through the beamcombiner 45 and some of the light beams 32 a,b,c are reflected by thebeam combiner 45. The metal layers should preferably have a thicknesswhich is less than the evanescent penetration depth of the light beams32 a,b,c to allow the light beams 32 a,b,c to be partially transmittedand partially reflected. Fresnel equations determine the amount of thelight beams 32 a,b,c which is reflected and transmitted by the beamcombiner 45.

The virtual image is formed behind the beam combiner 45. The light beams32 a,b,c reflected by the convex reflective projections 39 are divergingand are incident on the beam combiner 45. The light beams which arereflected by the beam combiner 45 remain divergent after the reflection.A virtual image 48 is formed at the position where extrapolations of thedivergent light beams which are reflected by the beam combiner 45intersect (the intersection will occur at a position which is behind thebeam combiner 45).

After the light beams 32 a,b,c have been reflected by the convexreflective projections 39 in the reflective element 38 the light beams32 a,b,c will be diffused. Each of the diffused light beams 32 a,b,cwill form a light cone. At least part of the diffused light beams 32a,b,c are reflected by the beam combiner 45. The eyebox 47 is defined bythe volume in which the light cones of all the light beams 32 a,b,cwhich are reflected by the convex reflective projections 39 on thereflective element 38 and subsequently reflected by the beam combiner45, overlap. If a viewer's eye is located in the eyebox 47 it willreceive at least one light ray which defining each of the pixels of thevirtual image 48; accordingly the full virtual image 48 will be seen bythe viewer. If a viewer's eye is located outside of the eyebox 47 theviewer's eye will receive light rays which define only some (or none) ofthe pixels of the virtual image 48; in this case the viewer will seeonly part (or no part) of the virtual image 48. For a viewer to see thefully virtual image their eye must be located within the eyebox 47.

It will be understood that in a further variant of the invention thebeam combiner may be integral to a windshield (for example thewindshield of a vehicle).

Advantageously in the projection device 30 shown in FIG. 1, thereflective element 38 acts as a diffuser to diffuse the light beams 32a,b,c and reduce the occurrence of speckle in the virtual image 48. Asthe light beams 32 a,b,c are reflected by the convex reflectiveprojections 39 in the reflective element 38 the light beams 32 a,b,c donot transmit through an optical component (e.g. they are not transmittedthrough the holder 43 of the micro-lens array 52); accordingly there isno diffraction of the light beams 32 a,b,c and there is a reduction theamount of light loss and parasitic light. Additionally, since the lightbeams 32 a,b,c are not transmitted through an optical componentconsequently a reduction in the amount of chromatic aberration generatedis achieved. Moreover the projection device 30 obviates the need for anyholder portion 43 and a micro-lens array 52 since it is the reflectiveelement 38 only which is used to reflect the light beams 32 a,b,c; thusa reduction in the number of parts of the projection device 30 can beachieved by providing a projection device which comprises the reflectiveelement 38 only without a micro-lens array 52 or holder 48.Additionally, since the convex reflective projections 39 in thereflective element 38 are convex, they are easier to manufacture thanmicro-lens arrays which comprise concave micro-lenses, as there is norequirement to provide pointed interfaces between the convex reflectiveprojections. Accordingly, it is easier to manufacture the projectiondevice 30. Furthermore, since the convex reflective projections 39 inthe reflective element 38 are convex, the light beams 32 a,b,c will bediffused rather than focused. Accordingly, the danger posed to a user'seyes is reduced. Finally, as the light beams are reflected by the convexreflective projections s 39 in the reflective element 38, the focalpoint of the reflective element 38 is located behind the convexreflective projections 39 of the reflective element 38. Accordingly, thetotal length of the projection device 30 can be reduced by an amountequal to twice the focal length of the reflective element 38 to providea more compact projection device.

FIG. 2 provides an aerial view of a projection device 50 according to afurther embodiment of the present invention. The projection device 50has many of the same features as the projection device 30 shown in FIG.1 and like features are awarded the same reference numbers.

In the projection device 50, further comprises converging lenses 61a,b,c which are arranged to receive the light beams 32 a,b,c which areoutput from the respective red, green and blue light sources 33 a,b,c,and which collimate the light beams 32 a,b,c used to provide collimatedlight beams 62 a,b,c which is output from the light source 31. Thedistance between the red, green and blue light sources 33 a,b,c and eachof the converging lenses 61 a,b,c is preferably equal to the focallength of the respective converging lens 61 a,b,c.

The MEMS micro mirror 34 receives collimated light beams 62 a,b,c fromthe light source 31.

The projection device 50 further comprises a telecentric lens 65 whichis arranged between the MEMS micro mirror 34 and the reflective element38. The telecentric lens 65 will focus the collimated light beams 62a,b,c and will also make the light beams 62 a,b,c parallel. In otherwords the telecentric lens 65 will make chief rays (or central ray) ofeach of the collimated light beams 62 a,b,c parallel to each other,while each of the individual collimated light beams 62 a,b,c are focusedonto the reflective element 38. The telecentric lens 65 is configured tofocus the collimated light beams 62 a,b,c such that the light beams 62a,b,c have a spot size on the micro-lens array 38 which has an areawhich is less than, or equal to, the area of a single convex reflectiveprojection 39 in the reflective element 38. Preferably, the area of thespot size will be 100 μm or less.

It will be understood that it is not necessary for the telecentric lens65 to be physically located between the MEMS micro mirror 34 and thereflective element 38; it would be sufficient for the telecentric lens65 to be located in an optical path followed by the light beams 62 a,b,cpassing from the MEMS micro mirror 34 to the reflective element 38.

FIG. 3 shows an aerial view of a projection device 100 according to afurther embodiment of the present invention. The projection device 100has many of the same features of the projection device 30 shown in FIG.1 and like features are awarded the same reference numbers.

In the projection device 100 the beam combiner 81 is configured to befully reflective. The projection device 100 further comprises asemi-reflective semi-transparent surface 82 which is provided on awindshield 83. The windshield 83 may be the windshield of a vehicle suchas a car or motorbike. The semi-reflective semi-transparent 82 surfaceis arranged to receive light beams 32 a,b,c which are reflected by thefully reflective beam combiner 81. The beam combiner 81 may be madefully reflective by providing the beam combiner 81 with a metal coating(thicker than the evanescent field penetration depth of the light beams32 a,b,c) or by providing the beam combiner 81 with a reflectivedielectric coating which has a bandgap in the wavelength range ofinterest.

The semi-reflective semi-transparent surface 82 on the windshield 83reflects some of the light beams 32 a,b,c which it receives from thebeam combiner 81. The light beams 32 a,b,c which are reflected by thesemi-reflective semi-transparent surface 82 are used to project avirtual image 48. The parts of the light beams 32 a,b,c which aretransmitted through the semi-reflective semi-transparent surface 82 arelost and are not used. The light beams which the semi-reflectivesemi-transparent surface 82 reflects are directed to a predefined areareferred to an eyebox 47. A user 49 can view the projected virtual image48 only when they look at the virtual image 48 from a location withinthe eyebox 47.

After the light beams have been reflected by the convex reflectiveprojections 39 in the reflective element 38 the light beams 32 a,b,cwill be diffused. Each of the diffused light beams 32 a,b,c will form alight cone. After the light beams 32 a,b,c have been reflected by theconvex reflective projections 39 in the reflective element 38 the lightbeams 32 a,b,c will be diffused. Each of the diffused light beams 32a,b,c will form a light cone. At least some of the diffused light beams32 a,b,c are reflected by the semi-reflective semi-transparent surface82. The eyebox 47 is defined by the volume in which the light cones ofall the light beams which are reflected by the convex reflectiveprojections 39 on the reflective element 38 and subsequently reflectedby the semi-reflective semi-transparent surface 82, overlap. The size ofthe eyebox 47 depends on the range of angles over which thesemi-reflective semi-transparent surface 82 can receive light from thefully reflective beam combiner 81. This range of angles may depend onthe size of the semi-reflective semi-transparent surface 82, on thedistance between the beam combiner 81 and the semi-reflectivesemi-transparent surface 82 and on the distance between the virtualimage 48 and semi-reflective semi-transparent surface 82. For example, alarge semi-reflective semi-transparent surface 82 can receive light fromthe beam combiner 81 over a large range of angles, accordingly thevolume in which all light cones overlap will be large and the thus theeyebox 47 will be large; while a smaller semi-reflectivesemi-transparent surface 82 can receive light from the beam combiner 81over a smaller range of angles, accordingly the volume in which alllight cones overlap will be small and the thus the eyebox 47 will besmall.

Some of light beams 32 a,b,c are reflected by the semi-reflectivesemi-transparent surface 82 on the windshield 83 and another some of thelight beam 32 a,b,c are transmitted through the semi-reflectivesemi-transparent surface 82 on the windshield 83. The light beams whichare reflected by the semi-reflective semi-transparent surface 82 remaindivergent after the reflection. The virtual image 48 is formed behindthe semi-reflective semi-transparent surface 82 on the windshield 83.The light beams reflected by the convex reflective projections 39 of thereflective element are diverging and are indecent on beam combiner 81where they are reflected to the semi-reflective semi-transparent surface82. The light beams which are reflected by the semi-reflectivesemi-transparent surface 82 remain divergent after they are reflected bythe semi-reflective semi-transparent surface 82. A virtual image 48 isformed at the position where extrapolations of the divergent light beamswhich are reflected by the semi-reflective semi-transparent surface 82intersect (the intersection will occur at a position which is behind thesemi-reflective semi-transparent surface 82). The light beams which aretransmitted through the semi-reflective semi-transparent surface 82 arelost and are not used to form the virtual image 48.

As discussed, the MEMS micro mirror 34 used in each of the projectiondevices 30,50,100 shown in FIGS. 1-3 may be configured either tooscillate about a single oscillation axis 7 only, to scan the lightbeams 32 a,b,c in one-dimension (i.e. along either the vertical orhorizontal directions), or configured to oscillate about two orthogonalaxes 7,17 to scan the light beams 32 a,b,c in two-dimensions (i.e. alongboth the vertical and horizontal directions). Or alternatively, in orderto scan the light beams 32 a,b,c in two-dimensions, the projectiondevices 30,50,100 may be provided with two MEMS micro mirrors 34, eachof which can oscillate about a single oscillation axis, and wherein theMEMS micro mirrors 34 are arranged to be in optical communication andsuch that their oscillation axes are orthogonal to one another; in thiscase one of the MEMS micro mirrors can be used to scan the light beams32 a,b,c in the vertical direction; the light beams 32 a,b,c which arescanned in the vertical direction are received by the other MEMS micromirror; the other MEMS micro mirror oscillates to scan the light beams32 a,b,c in the horizontal direction, thus achieving two-dimensionalscanning of the light beams 32 a,b,c.

FIGS. 4a and 4b show a MEMS micro mirror 34 a which is configured tooscillate about a single oscillation axis 7 and FIG. 4c shows a MEMSmicro mirror 34 b which is configured to oscillate about a twoorthogonal oscillation axes 7,17. The MEMS micro mirror 34 used in theprojection device 30,50,100 may be configured as the MEMS micro mirror34 a shown in FIGS. 4a and 4b , or may be configured as the MEMS micromirror 34 b shown in FIG. 4c . It will be understood that the projectiondevice 30,50,100 may be provided with two MEMS micro mirrors 34 eachconfigured as the MEMS micro mirror 34 a shown in FIGS. 4a and 4b , andthe two MEMS micro mirrors being arranged to be in optical communicationand such that their oscillation axes are orthogonal.

Referring to FIGS. 4a and 4b ; FIG. 4a provides a plan view of the MEMSmicro-mirror 34 a and FIG. 4b shows a cross sectional view of the MEMSmicro-mirror 34 a, taken along A-A′ of FIG. 4a . The MEMS micro-mirror34 a is shown to comprise a first support frame 2. A first torsional arm3 a and second torsional arm 3 b connect a mirror 4 to the support frame2. The support frame 2 is fixed (i.e. immovable). The first and secondtorsional arms 3 a,b define a first oscillation axis 7 for the mirror 4.A first actuation coil 5 is supported on, and connected to, the mirror4. The first actuation coil 5 is arranged to extend, from a firstelectrical contact 9 a which is located on the support frame 2, alongthe first torsional arm 3 a, and around the perimeter of the mirror 4and back along the first torsional arm 3 a to a second electricalcontact 9 b which is located on the support frame 2.

The first support frame 2, first and second torsional arms 3 a,b and theMEMS micro mirror 4, and first actuation coil 5, define collectively aMEMS die 10. As shown in FIG. 4b , the MEMS die 10 is supported on amagnet 6 such the first actuation coil 5 is submerged in the magneticfield ‘B’ generated by the magnet 6.

During use an electric current ‘I’ is passed through the first actuationcoil 5. As the first actuation coil 5 is submerged in the magnetic field‘B’ created by the magnet 6, the actuation coil 5 will provide a Laplaceforce which will be applied to the mirror 4. The Laplace force willcause the mirror 4 to oscillate about its first oscillation axis 7. Themirror 4 may reflect light beams 32 a,b,c, 62 a,b,c it receives as itoscillates, thereby scanning the light beams 32 a,b,c, 62 a,b,c inone-dimension.

If a first and second MEMS micro mirror, each with the same features asthe MEMS micro mirror 34 a shown in FIG. 4a , are arranged in opticalcommunication, and arranged such that the oscillation axes 7 of bothmirrors 4 are orthogonal, then the light beams 32 a,b,c, 62 a,b,c can bescanned by the MEMS micro mirrors, in two-dimensions (typically alongthe horizontal and vertical). Alternatively, to enable light beams 32a,b,c, 62 a,b,c to be scanned in two-dimensions the mirror 4 in the MEMSmicro mirror 34 may be configured to oscillate about two orthogonaloscillation axes 7,17. FIG. 4c shows a MEMS micro mirror 34 b which isconfigured to oscillate about two orthogonal oscillation axes 7,17.

The MEMS micro-mirror 34 b has many of the same features of the MEMSmicro-mirror 34 a shown in FIGS. 4a and 4b ; however in the MEMSmicro-mirror 34 b the support frame 2 is configured to be moveable; thesupport frame 2 is configured such that it can oscillate about a secondoscillation axis 17, which is orthogonal to the first oscillation axis7.

The MEMS micro-mirror 34 b further comprises a fixed part 12 (i.e. animmovable part); the support frame 2 is connected to the fixed part 12via third and fourth torsional arms 13 a,b. The third and fourthtorsional arms 13 a,b, define the second oscillation axis 17. A secondactuation coil 15 is connected to the support frame 2. This secondactuation coil 15 will also be submerged by the magnetic field ‘B’generated by the magnet 6.

A second actuation coil 15 is supported on, and connected to, thesupport frame 2. The second actuation coil 15 is arranged to extend,from a first electrical contact 19 a which is located on the fixed part12, along the third torsional arm 13 a, around the perimeter of thesupport frame 2 and back along the third torsional arm 13 a to a secondelectrical contact 19 b which is located on the fixed part 12. It shouldbe noted that the second actuation coil 15 does not extend along thefourth torsional arm 13 b.

Furthermore, in the MEMS micro-mirror device 20 the first and secondelectrical contacts 9 a,9 b for the first actuation coil 5 are locatedon the fixed part 12, and thus the first actuation coil 5 is arranged toalso extend along the support frame 2 and the third and fourth torsionalarms in order to electrically connect to the first and second electricalcontacts 9 a,9 b.

During use an electric current ‘i’ is passed through the first actuationcoil 5 which is connected to the mirror 4. As the first actuation coil 5is submerged in the magnetic field ‘B’ created by the magnet 6 the firstactuation coil 5 will provide a Laplace force which will be applied tothe mirror 4. The Laplace force will cause the mirror 4 to oscillateabout the first oscillation axis 7. An electric current ‘I’ is alsopassed through the second actuation coil 15 which k connected to thesupport frame 2. As the second actuation coil 15 is also submerged inthe magnetic field ‘B’ created by the magnet 6, the second actuationcoil 15 will provide a Laplace force which will be applied to thesupport frame 2. The Laplace force which is applied to the support frame2 by the second actuation coil 15 will cause the support frame 2, andthus the mirror 4 which is connected to the support frame 2 via thetorsional arms 13 a,b, to oscillate about the second oscillation axis17. Accordingly the mirror 4 will be oscillated about the first andsecond orthogonal oscillation axes 7,17. If the mirror 4 reflects lightbeams as it is oscillating about the first and second orthogonaloscillation axes 7,17 the reflected light beams 32 a,b,c, 62 a,b,c willbe scanned in two dimensions e.g. horizontal and vertical.

If the MEMS micro mirror 34 provided in the projection devices 30,50,100is configured as the MEMS micro mirror 34 a shown in FIGS. 4a and 4b(i.e. if the MEMS micro mirror 34 is configured to oscillate about asingle oscillation axis 7), then the focus point of the light reflectedby the MEMS micro mirror 34 will move along a curve (i.e. an arc) as theMEMS micro mirror 34 oscillates about its single oscillation axis 7. Itshould be remembered that the in the projection device 30,50,100 thelight beams 32 a,b,c, 62 a,b,c are focused by means of the lenses 41a,b,c or telecentric lens 65 respectively. In the projection device30,50 the focus point of light reflected by the MEMS micro mirror is thefocal point of the lenses 41 a,b,c which is arranged between the lightsource and the MEMS micro mirror to focus the light beams 32 a,b,c; or,in the projection device 100 which comprises a telecentric lens 65 whichfocuses light beams, the focus point of light reflected by the MEMSmicro mirror is the focal point of the telecentric lens 65. Therefore,effectively, oscillation of the MEMS micro mirror 34 about a singleoscillation axis 7 will cause the focal point of the lenses 41 a,b,c orthe focal point of the telecentric lens 65 to move along a curve (arc)as the MEMS micro mirror 34 oscillates about its single oscillation axis7.

FIG. 5a illustrates that as the MEMS micro mirror 34 oscillates about asingle oscillation axis 7, the focus point (F) of the light reflected bythe MEMS micro mirror 34 is moved along a curve 150 (i.e. an arc 150).This occurs because the focus length (f) of the light reflected by theMEMS micro mirror 34 remains constant as the MEMS micro mirror 34oscillates about the single oscillation axis 7.

Likewise if the MEMS micro mirror 34 is configured as the MEMS micromirror 34 b shown in FIG. 4c (i.e. if the MEMS micro mirror 34 isconfigured to oscillate about two orthogonal oscillation axes 7,17) thenthe focus point of the light reflected by the MEMS micro mirror 34 willmove along a curved plane, more specifically the focus point of thelight reflected by the MEMS micro mirror 34 win move along aconcave-spherical or concave-aspherical plane.

It can be seen from FIG. 5a that because the position of the focus point(F) is moving along a curved plane, the position of the convexreflective projections 39 in the reflective element 38 will not alwayscorrespond to the position of focus point (F) of the light reflected bythe MEMS micro mirror 34. As a result the light beams 32 a,b,c, 62 a,b,cwill not be focused to a point on the convex reflective projections 39in the reflective element 38; this will result in a decrease in thequality of the virtual image 48.

FIGS. 5b and c shows preferred configurations for the reflective element38 used in the projection devices 30,50,100 shown in FIGS. 1-3. FIG. 5billustrates a first configuration for the reflective element 38 and FIG.5c illustrates a second configuration for the reflective element 38. Theconfigurations illustrated in FIGS. 5b and 5c can compensate for themovement of the focus point (F) of the light reflected by the MEMS micromirror 34 along a curved plane, which occurs when the MEMS micro mirror34 oscillates, so that the position of the convex reflective projections39 in the reflective element 38 will always correspond to position ofthe focus point (F) of the light reflected by the MEMS micro mirror 34.

FIG. 5b shows a preferred configuration for the reflective element 38when the projection device 30,50,100 comprises a single MEMS micromirror 34 which oscillates about a single oscillation axis 7 (i.e. theMEMS micro mirror 34 is configured as the MEMS micro mirror 34 a shownin FIGS. 4a and 4b ).

In the configuration illustrated in FIG. 5b , the convex reflectiveprojections 39 of the reflective element 38 are arranged to lie on acurved plane 120. The curved plane 120 is a concave plane. The curvatureof the curved plane 120 is equal to the curvature of the curve 150 (i.e.arc 150) along which the focus point (F) of the light reflected by theMEMS micro mirror 34 moves as the MEMS micro mirror 34 oscillates aboutits single oscillation axis 7. In this manner reflective element 38 cancompensate for the changes in the position of focus point (F) of MEMSmicro mirror 34, which occurs when the MEMS micro mirror 34 oscillatesabout its single oscillation axis 7. As the convex reflectiveprojections 39 of the reflective element 38 lie on a curved plane 120whose curvature is equal to the curvature of the curve 150 (i.e. arc150) along which the focus point (F) of the light reflected by the MEMSmicro mirror 34 moves as the MEMS micro mirror 34 oscillates about itssingle oscillation axis 7, the position of the convex reflectiveprojections 39 in the reflective element 38 will always correspond tothe position of focus point (F) of the light reflected by the MEMS micromirror 34. As a result the light beams 32 a,b,c, 62 a,b,c will befocused to a point on the convex reflective projections 39 in thereflective element 38, throughout the whole amplitude of oscillation ofthe MEMS micro mirror 34. As a result, the quality of the virtual image48 will not be compromised by the movement of the focus point (F) of thelight reflected by the MEMS micro mirror 34 along a curved plane, as theMEMS micro mirror 34 oscillates.

FIG. 5c shows a preferred configuration for the reflective element 38when the projection device 30,50,100 comprises a MEMS micro mirror 34which can oscillate about two orthogonal oscillation axes 7,17 i.e. theMEMS micro mirror 34 is configured as the MEMS micro mirror 34 b shownin FIG. 4c , (or, as the case may be, when the projection device30,50,100 comprises two MEMS micro mirrors 34 each configured as theMEMS micro mirror 34 a shown in FIGS. 4a and 4b , and each arranged inoptical communication with one another and such that the oscillationaxis of the two MEMS micro mirrors are orthogonal).

In the configuration illustrated in FIG. 5c , the convex reflectiveprojections 39 of the reflective element 38 are arranged to lie on aspherical plane 125, or more specifically a concave-spherical plane 125.The curvature of the concave-spherical plane 125 is equal to thecurvature of the concave-spherical plane along which the focus point (F)of the light reflected by the MEMS micro mirror 34 moves as the MEMSmicro mirror 34 oscillates about it two orthogonal oscillation axis 7,17(or, as the case may be, as the two MEMS micro mirrors which are inoptical communication and which have oscillation axes which areorthogonal, oscillate about their respective oscillation axes). In thismanner the reflective element 38 can compensate for the movement offocus point (F) of light reflected by the MEMS micro mirror 34 along theconcave-spherical plane, which occurs when the MEMS micro mirror 34oscillates about its two orthogonal oscillation axis 7,17. As the convexreflective projections 39 of the reflective element 38 lie on aconcave-spherical plane 125 whose curvature is equal to the curvature ofthe concave-spherical plane along which the focus point (F) of the lightreflected by the MEMS micro mirror 34 moves as the MEMS micro mirror 34oscillates about its two orthogonal oscillation axis 7,17, (or, as thecase may be, as the two MEMS micro mirrors which are in opticalcommunication and which have oscillation axes which are orthogonal,oscillate about their respective oscillation axes) the position of theconvex reflective projections 39 in the reflective element 38 willalways correspond to the position of focus point (F) of the lightreflected by the MEMS micro mirror 34. Thus the quality of the virtualimage 48 will not be compromised by the movement of the focal point (F)of the MEMS micro mirror 34 along the concave-spherical plane, as theMEMS micro mirror 34 oscillates.

It should be understood that in a another embodiment of the presentinvention, the focus point of the light reflected by the MEMS micromirror 34 may be moved along an concave-aspherical plane as the MEMSmicro mirror 34 oscillates. In such a case the convex reflectiveprojections 39 of the reflective element 38 may be arranged to lie on aconcave-aspherical plane. The curvature of the concave-aspherical planewill be equal to the curvature of the concave-aspherical plane alongwhich the focus point (F) of the light reflected by the MEMS micromirror 34 moves as the MEMS micro mirror 34 oscillates. This will ensurethat the position of the convex reflective projections 39 of thereflective element 38 will always correspond to the position of focuspoint (F) of the light reflected by the MEMS micro mirror 34. Thus thequality of the virtual image 48 will not be compromised by the movementof the focus point (F) of the light reflected by the MEMS micro mirror34, along the concave-aspherical plane, as the MEMS micro mirror 34oscillates. FIG. 6a illustrates the beam combiner 45,81 used in theprojection devices 30,50,100 shown in FIGS. 1-3. It can be seen fromFIG. 6a that the beam combiner 45,81 has a curved profile. As alreadyillustrated in FIGS. 1-3, the concave surface 46 of the beam combiner45,81 receives the light beams 32 a,b,c 62 a,b,c from the reflectiveelement 38.

The curved beam combiner 45,81 will define a curved focal plane 200(i.e. the focal plane 200 is a plane defined by focal points ofdifferent areas of the beam combiner 45,81). The curved combiner 45,81will thus focus the virtual image 48 onto the curved focal plane 200. Asa result the virtual image 48 will appear distorted or blurred. The beamcombiner 45,81 has a curved profile to specify the position of the focalplane 200 and to adapt the position and size of the virtual image 48 sothat it is comfortable for the viewer 49.

FIG. 6b shows an alternative configuration for the reflective element 38which may be used in the projection devices 30,50,100 shown in FIGS.1-3, to compensate for the effect of the curved beam combiner 45,81.

In the configuration for the reflective element 38 shown in FIG. 6b ,the convex reflective projections 39 of the reflective element 38 arearranged to lie on a convex curved plane 250. The curvature of theconvex curved plane 250 on which the convex reflective projections 39 ofthe reflective element 38 lie, is such that focal points (F) of allareas of the beam combiner 45,81 will lie on the same planar plane. Inthis particular example the curvature of the convex curved plane 250 onwhich the convex reflective projections 39 of the reflective element 38lie, is preferably equal to the curvature of the concave surface 46 ofthe beam combiner 45,81 which receives the light beams 32 a,b,c 62 a,b,cfrom the reflective element 38. The configuration for the reflectiveelement 38 shown in FIG. 6b will thus compensate for the effect of thecurved beam combiner 45,81, thereby ensuring that the virtual image 48will appear to be on a planar plane so that virtual image 48 will appearclearer to a viewer.

It should noted that any one of the projection devices 30,50,100 may beused to provide a head-up-display projection system. In the case theprojection devices 30,50 are used to provide the head-up-displayprojection system the beam combiner 45 may be used as thehead-up-display. In the case the projection device 100 is used toprovide the head-up-display projection system the semi-reflectivesemi-transparent surface 82 which is provided on a windshield 83 may beused as the head-up-display.

Various modifications and variations to the described embodiments of theinvention will be apparent to those skilled in the art without departingfrom the scope of the invention as defined in the appended claims. Forexample, in the projection devices 30,50,100 shown in FIGS. 1a -3,although the MEMS micro mirror of the projection device 30 is shown tobe offset from the centre of the reflective element 38 it will beunderstood that the MEMS micro mirror could be aligned with the centreof the reflective element 38.

An additional variation is that the projection devices 30,50,100 mayeach further comprise an imaging system such as DLP/DMD (Digital LightProcessing/Digital Micromirror array), LCOS (Liquid Crystal on Silicon)and/or LCD (Liquid Crystal Display); the reflective element may bearranged so that the convex reflective projections direct light to theimaging system. In this case the pixels of the image are defined by theimaging system using the light beams. Because the light beams arescanned by the oscillating MEMS mirror onto the reflective element, thenas a result the light reflected by the convex reflective projections isdespeckled and therefore can serve as illuminating source which providesdespeckled light to the second imaging device or to any random surface

Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiment.

1-15. (canceled)
 16. A projection device comprising: a reflectiveelement comprising a plurality of convex reflective projections, theplurality of convex reflective projections disposed on a curved plane: aMEMS micro mirror to receive a plurality of light beams, the MEMS micromirror to oscillate about at least one oscillation axis to scan theplurality of light beams onto the reflective element, the plurality ofconvex reflective projections to reflect the plurality of light beamsincident on the plurality of convex reflective projections; and a beamcombiner to receive the plurality of light beams reflected by the convexreflective projections and to at least partially reflect the pluralityof light beams to form a virtual image to be viewed from within aneyebox.
 17. The projection device of claim 16, comprising a light sourceto provide the plurality of light beams.
 18. The projection device ofclaim 17, comprising one or more lenses disposed between the lightsource and the MEMS micro mirror to focus the plurality of light beams.19. The projection device of claim 16, wherein the reflective element isarranged such that the convex reflective projections are closer to theMEMS micro mirror than any other part of the reflective element.
 20. Theprojection device of claim 16, wherein the beam combiner issemi-reflective and semi-transparent, and wherein the plurality of lightbeams reflected by the beam combiner define the virtual image viewablefrom within the eyebox.
 21. The projection device of claim 16, whereinthe beam combiner is fully reflective, the projection device comprisinga semi-reflective semi-transparent surface to receive the plurality oflight beams reflected by the beam combiner and to partially reflect theplurality of light beams to define the virtual image.
 22. The projectiondevice of claim 21, wherein the semi-reflective semi-transparent surfaceis a windshield or a visor.
 23. The projection device of claim 16,wherein the plurality of light beams are collimated light beams, theprojection device comprising a telecentric lens disposed between theMEMS micro mirror and the reflective element to focus the collimatedlight beams.
 24. The projection device of claim 16, wherein theplurality of light beams are focused to have a spot size on thereflective element, the spot size to have an area that is less than, orequal to, the area of a one of the plurality of convex reflectiveprojections.
 25. The projection device of claim 16, wherein the curvedplane is a convex-spherical plane, a convex-aspherical plane, aconcave-spherical, or a concave-aspherical plane.
 26. The projectiondevice of claim 16, wherein the beam combiner has a curved profile. 27.A system comprising: a light source to provide a plurality of lightbeams; a reflective element comprising a plurality of convex reflectiveprojections, the plurality of convex reflective projections disposed ona curved plane: a MEMS micro mirror to receive the plurality of lightbeams, the MEMS micro mirror to oscillate about at least one oscillationaxis to scan the plurality of light beams onto the reflective element,the plurality of convex reflective projections to reflect the pluralityof light beams incident on the plurality of convex reflectiveprojections; a beam combiner to receive the plurality of light beamsreflected by the convex reflective projections; and a semi-transparentprojection surface to receive the plurality of light beams reflectedfrom the beam combiner and to at least partially reflect the pluralityof light beams to form a virtual image to be viewed from within aneyebox.
 28. The system of claim 27, wherein the semi-transparent surfaceis a windshield or a visor.
 29. The system of claim 27, wherein thereflective element is oriented such that the plurality of light beamsreflected from the MEMS micro mirror to the reflective element when theMEMS micro mirror is at rest are incident on the reflective element atan angle that is non-perpendicular to a plane of the reflective element.30. The system of claim 27, comprising at least one of a Digital LightProcessing Array, a Digital Micromirror Array, a Liquid Crystal onSilicon, or a Liquid Crystal Display, the at least one of a DigitalLight Processing Array, a Digital Micromirror Array, a Liquid Crystal onSilicon, or a Liquid Crystal Display to receive the plurality of lightbeams reflected from the reflective element and to reflect the pluralityof light beams to the beam combiner.
 31. The system of claim 27, whereinthe plurality of light beams are focused to have a spot size on thereflective element, the spot size to have an area that is less than, orequal to, the area of a one of the plurality of convex reflectiveprojections.
 32. The system of claim 27, wherein the curved plane is aconvex-spherical plane, a convex-aspherical plane, a concave-spherical,or a concave-spherical plane.
 33. A method to project a virtual image,the method comprising: receiving, at a reflective element, a pluralityof light beams, the reflective element comprising a plurality of convexreflective projections disposed on a curved plane: reflecting, at theplurality of convex projections, the plurality of light beams;receiving, at a beam combiner, the plurality of light beams reflectedfrom the plurality of convex reflective projections; and at leastpartially reflecting, at the beam combiner, the plurality of light beamsto form a virtual image to be viewed from within an eyebox.
 34. Themethod of claim 33, comprising providing the plurality of light beams.35. The method of claim 33, comprising: receiving, at a semi-transparentprojection surface, the plurality of light beams reflected from the beamcombiner; and at least partially reflecting, at the semi-transparentprojection surface, the plurality of light beams to form the virtualimage.